Trunking

I noticed that my scanner offers trunking support. It says that it can monitor like up to 4 channels at a time.

I was wondering, could I use this feature to monitor both channels on a railroad that has 2 different channels like CN?

Any thoughts on how?

Short: No.

Long:
Traditional radio equipment works because all parties involved in the communication agree on what frequencies they will utilize. Traditional radio scanners work by scanning for and then listening to those frequencies.

Trunking radios, on the other hand, constantly renegotiate the frequencies utilized for the conversation. This allows for more efficient utilization of limited frequencies because each conversation does not require a dedicated channel. However, it also makes it very difficult to scan trunked conversations because you do not usually know what frequency the next portion of the conversation will appear on.

Trunked radio systems are utilize one or more "Control" or "Data" channels. The data passed via the control channel instructs each radio in the system which frequency to switch to in order to remain on the selected channel. Several utilities are available to monitor and decode some of the common trunking protocols:

Keeper1616 gave a very good general explanation of how trunking works. Let me try to add a little more...

Trunking is really intended for high-volume use where there are many users or groups that need to have radio access. In a trunk system each user or group is assigned a talkgroup ID that is programmed into all the radios in that system-base, portables, and mobiles. The system itself is assigned a certain number of frequencies with one or two marked as the Control or Data channels. Once you have a trunk-capable scanner properly programmed with all the frequencies and talkgroup ID's you'll be able to monitor a trunked system just like a conventional 2-way radio system. When scanning trunk systems my 2 Bearcat BC-895's show only the talkgroup ID on the display. On the other hand my 2 Bearcat BC-780's show the talkgroup ID, the talkgroup alpha tag, and the frequency in use. As the conversation progresses the talkgroup ID and alpha tag stay the same but you'll see the frequency change each time the microphone gets keyed.

At this time there are no railroads I'm aware of who use trunking for their rail operations. All you need to do is program the frequencies of what you want to listen to, sit back, and enjoy.